The invention herein resides in the art of tire molding apparatus and techniques. More particularly, the invention relates to a ventless tire mold. More specifically, the invention presents a ventless tire mold which is made of a plurality of interconnecting pitches, with the interface of the pitches serving as vent lines for the mold cavity.
It is well known that the manufacture of pneumatic tires typically requires the implementation of a mold and associated tire presses to form the tire tread in the green rubber and to hold the tire configuration while the green tire cures. In the past, the preparation of tire molds has generally been extremely labor intensive and involved highly skilled manual labor, both resulting in significant cost in the development of a tire mold.
In the past, it has generally been known to employ a hand carver a computerized numeric controller (CNC) machine to make a master model of an appropriate material such as REN board, plaster, or the like. From the master model, foundry tooling is made and ultimately from the foundry tooling cores are developed. As is understood by those skilled in the art, a core is a sequence of pitches or tire tread elements. An appropriate number of cores with the requisite pitch sequences for the desired tread pattern were necessarily generated. These cores were then mated in the proper diameter and pitch sequence to define the requisite mold. This assembly was then cured and employed to make castings, from which the molds themselves could ultimately be made.
In the prior art process of casting tire cores, a number of shortcomings were present. Generally, undercuts were inpossible to achieve except by tedious handwork. However, such undercuts are common in tire designs where sipes must be employed. Additionally, prior art molds necessarily required a large number of pinhole vents to allow air to escape from the mold as the tire was expanded into the mold during the curing operation. These pinhole vents required continuous cleaning and removal of cured rubber to prevent such blockage from impairing the efficiency of the mold.
As one can readily appreciate, these prior art mold designs are extremely time consuming and costly to manufacture, implement and maintain. Accordingly, there is a need in the art for a tire molding apparatus and technique which overcomes these shortcomings of the prior art.
In light of the foregoing, it is a first aspect of the invention to provide a tire molding apparatus and technique which is of a ventless nature.
Another aspect of the invention is the provision of a tire molding apparatus and technique in which segments of the tire mold are assembled single pitches, rather than cores.
Still a further aspect of the invention is the provision of tire molding apparatus and technique in which the venting of the mold is at the pitch line formed at the intersection of mating pitches, rather than through the addition of pinhole vents.
Still a further aspect of the invention is the provision of a tire molding apparatus and technique in which a model is made of a REN board, plaster or the like, sipes are set in the model itself then traditional master rubbers can be made.
A further aspect of the invention is the presentation of a tire molding apparatus and technique in which a mold may be developed by casting of single pitches, rather than entire cores.
Still a further aspect of the invention is the provision of a tire molding apparatus and technique which is readily conducive to implementation with state of the art materials and processes.
The foregoing and other aspects of the invention which will become apparent herein are achieved by a ventless tire mold, comprising: a plurality of mold segments nestingly interconnecting with each other at segment interferences to form an annular mold, said segment interfaces defining air passages from an interior of said annular mold.
Other aspects of the invention which will become apparent herein are attained by a method for making a ventless tire mold, comprising: (a) developing three dimensional models of tire tread portions; (b) installing sipes into the models; (c) generating foundry castings from the siped models; (d) preparing individual pitch profiles from said foundry castings; and (e) assembling a mold by nestingly interconnecting a plurality of said prepared individual pitch profiles.